Jar device for use in coil tubing drilling

ABSTRACT

The invention relates to a jar operated by fluid pressure, specially designed for use in drilling or maintenance operations carried out in oil or gas wells. The jar comprises a first ( 1 ) and a second ( 2 ) end piece, where the second end piece ( 2 ) comprises a jar shoulder ( 15 ), an inner, cylindrical string part ( 8 ) connected to a valve head ( 9 ) with a first valve surface ( 14 ), and to a weight ( 12 ), an outer, cylindrical string part ( 17 ), arranged axially movably to the inner cylindrical string part ( 8 ), and comprising a second valve surface ( 30 ), which is arranged to go into abutment against the first valve surface ( 14 ) on the valve head ( 9 ). The jarring function is achieved by the inner string part ( 8 ) and thereby the weight ( 12 ) being set in axial motion and striking the shoulder ( 15 ).

FIELD OF THE INVENTION

The present invention relates to a jar operated by liquid pressure, especially of the type that is preferably employed in connection with drilling or maintenance operations carried out in oil or gas wells.

BACKGROUND OF THE INVENTION

According to current technology, oil and/or gas wells are essentially drilled with a rotating drill string and a drill bit mounted in the bottom of the drill string. In some cases use is made of a continuous drill string (coil tubing) coiled up on a roller. The coil tubing is lowered into and retrieved from the borehole by an injector. At the bottom of the coil tubing there is often a liquid motor which rotates the bit by means of drilling mud that is pumped down through the coil tubing. A signal cable for direction control and guidance is often lowered through the centre hole in the coil tubing.

Coil tubing is also used in connection with maintenance of production wells which have been in production for some time and which need to be cleaned up in order to maintain production.

Such cases often involve the removal of deposits left in pipe systems. For carrying out this type of operation it has been shown to be expedient to use jar technology to remove deposits. A jar is also used in connection with special operations such as setting plugs, “fishing” operations, etc.

The jar is placed in the bottom of the coil tubing and operated by fluid that is pumped down through the coil tubing.

Present day jar technology has proved to be inefficient with regard to the functional requirements for the work that requires to be performed.

U.S. Pat. No. 5,033,557 discloses a previously known fluid-operated jar for use in a well.

SUMMARY OF THE INVENTION

With the present invention a jar design has been attained that makes it possible to achieve greater efficiency and better reliability through a simplified and more robust construction. The invention also represents a simplification of production, thus making the product cheaper and thereby enabling it to be used in several situations where economic criteria are critical.

The present invention represents substantial improvements compared to current technology with regard to functionality, efficiency, reliability and economy.

The objects and advantages of the invention are achieved with a jar as indicated in the following independent claim 1.

Further advantageous features will become evident from the following dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail by describing a preferred embodiment and with reference to the attached drawings, in which:

FIG. 1 is a perspective view illustrating a jar according to the invention,

FIG. 2 is a partly cut away perspective view illustrating a section through the jar structure, and

FIG. 3 is a further perspective view illustrating a detail section of the valve system in the jar.

Identical reference numerals are employed for identical elements in the drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a perspective view illustrating a jar according to the invention.

At its first end the jar comprises a first end piece 1 with a first adapter, which is provided with threads for connecting to a coil tubing or other tool. The jar further comprises an outer, cylindrical casing 5, 4, 3. The casing 5, 4, 3 is preferably in three parts, comprising a first, outer cylindrical casing element 5 provided with a number of openings 6, which is further connected to a cylindrical spacer 4, which in turn is connected to a second, outer casing element 3. The second casing element 3 is also provided with a number of openings 7. The second casing element 3 is further connected to a second end piece 2. The second end piece 2 comprises a second adapter, which like the first adapter 1 is provided with threads for connecting to a coil tubing or other tool.

FIG. 2 is a partly cut away perspective view illustrating a section through the jar structure. In order to elucidate the internal construction of the jar, in FIG. 2 the first 5 and the second 3 cylindrical casing elements, as well as the spacer 4 are shown partly cut away.

Further details of the jar's internal construction, including the valve system, are illustrated in FIG. 3.

The jar comprises an internal hollow, through-going, cylindrical, central string part 8.

The central string part 8 is connected to an enclosing valve head 9. The valve head 9 is provided with a valve surface 14.

The central string part 8 is further attached to an enclosing, cylindrical weight 12. The central string part 8, the valve head 9 and the weight 12 are together arranged to be able to be moved axially in a rectilinear forward and backward motion.

The jarring effect is produced by the weight 12, which is attached to the associated, central string part 8, being set in an axially forward and backward motion, thus causing the weight 12 to strike the shoulder 15 on the end piece 2.

In order to provide the forward and backward motion, liquid under pressure is employed, supplied from the central string part 8. The fluid is passed through the openings 16 in the central string part 8 and on through openings 29 in an outer, cylindrical string part 17, which is concentrically mounted on the internal cylindrical string part 8.

The outer string part 17 is provided with a conical valve surface 30 which is arranged to go into abutment against the first valve surface 14 arranged on the valve head 9.

The outer string part 17 is further provided with a seal 24 against the outer casing element 5 and a seal 25 against the spacer 4. A seal is provided against the inner cylindrical string part 8 by seal elements 26 and 27 which are mounted between the inner 8 and the outer 17 string part.

A first spring or main spring 10 is mounted enclosing the inner string part 8, on the inside of the outer casing element 5. Without liquid pressure, which is implicitly understood in the inner cylindrical string part 8, the main spring 10 will push both the inner 8 and the outer 17 cylindrical string part axially, thus causing the shoulders 18 to abut against each other. In this position the first valve surface 14 will simultaneously provide a seal against fluid flow.

When fluid pressure is applied by pressurising the inner cylindrical string part 8, this will influence the piston area between the seals 24, 25 and 26, 27, thus causing both the inner 8 and the outer 17 cylindrical string parts to move axially and be pushed against the main spring 10 with the first valve surface 14 in abutment.

When the movement has reached the point where the shoulders 21 and 22 are in abutment against each other, this causes the movement of the outer string part 17 to stop. In this position the sealing element 20 will go into abutment against the shoulder 19. At the same time the second spring 11, which is arranged axially enclosing the outer string part 17 on the inside of the second outer casing element 3, has been pretensioned since the second spring's end piece 28, which is attached to the outer string part 17, has moved axially as a result of the movement of the outer string part 17.

The inner string part 8 with associated valve head 9 continues the movement as the pressure continues to rise, and the valve surface 14 begins to open for through-flow through the openings 23. The sealing element 20 simultaneously abuts against the shoulder 19.

This results in a pressure equalisation on both sides of the seal 24, causing the outer string part 17 to accelerate by means of the second spring 11 and open the valve fully, while the openings 16 and 29 are moved relative to each other, thereby providing a seal against in going fluid flow from the inner string part 8.

The spring force of the springs 10 and 11 is arranged in such a manner that the second spring 11 holds the valve surfaces apart during the entire percussive motion, which is terminated by the inner string part 8 with the weight 12 striking the shoulder 15 on the end piece 2, and the valve surface 14 is again closed against the valve surface 30 on the inner string part 8. At the same time the inner 8 and outer 17 cylindrical string parts are moved axially, thus causing the openings 16 and 29 to once again be opposite each other, and a new stroke begins.

The liquid displaced by movement of the inner 8 and the outer 17 cylindrical string parts is discharged through the opening's 6. The openings 7 act as pressure equalisation against surrounding fluid when the weight 12 is set in motion.

An essential condition for achieving the jarring function with forward and backward motion is that the opening sequence for the valve surface 14 and the valve surface

is combined with approximately simultaneous closing by the sealing element 20, thereby achieving pressure equalisation on the piston area a short time before the valve opens fully and the main spring accelerates both the string parts 8 and 17.

During use the jar is mounted in the well below the coil tubing. It will be apparent from the above that the coil tubing can be connected either to the first adapter 1 or the second adapter 2 on the jar. In both cases the jarring movement will be directed towards the end piece at the second adapter 2. It will therefore be evident that the resulting jarring movement is directed from the coil tubing, i.e. downwards in the well, if the coil tubing is connected to the first adapter 1, while the jarring movement will be directed towards the coil tubing, i.e. upwards in the well, if the coil tubing is connected to the second adapter 2.

There will be a through-going fluid passage between the first 1 and the second 2 connection adapter. It will be understood that the adapter that is not connected to the coil tubing may advantageously be connected to another tool for use in well drilling and/or well maintenance operations. 

1. A jar operated by liquid pressure, specially designed for use in drilling or maintenance operations carried out in oil or gas wells, characterised in that it comprises a first (1) and a second (2) end piece, where the second end piece (2) comprises a jar shoulder (15), an inner, cylindrical string part (8) connected to a valve head (9) with a first valve surface (14), and to a weight (12), an outer, cylindrical string part (17), arranged axially movably to the inner cylindrical string part (8), comprising a second valve surface (30), which is arranged to go into abutment against the first valve surface (14) on the valve head (9), where jarring function is achieved by the inner string part (8) and thereby the weight (12) being set in axial motion and striking the shoulder (15).
 2. A jar according to claim 1, where the outer cylindrical string part (17) is concentrically enclosing the inner cylindrical string part (8).
 3. A jar according to one of the claims 1-2, where the outer cylindrical string part (17) is further provided with openings (23).
 4. A jar according to one of the claims 1-3, where on the valve head (9) there is mounted a sealing element (20) for abutment and flexible sealing against the shoulder (19).
 5. A jar according to one of the claims 1-4, where between the inner (8) and the outer cylindrical string parts (17) there are provided openings (16, 29) for opening and closing ofthrough-flow.
 6. A jar according to one of the claims 1-5, further comprising an outer, cylindrical casing (3, 4, 5) connected between the first (1) and the second (2) end piece.
 7. A jar according to claim 6, where the outer cylindrical casing (3, 4, 5) comprises a first casing element (5) connected to a spacer (4), further connected to a second casing element (3).
 8. A jar according to claim 4, designed to cause opening of the first valve surface (14) to approximately coincide with closing by the sealing element (20). 